FR2827242A1 - Hydraulic brake for motor vehicle has vent for master cylinder to prevent brake pedal return after impact in accident - Google Patents

Abstract

The hydraulic brake for a motor vehicle has two brake circuits (3,4) fed separately by a common master cylinder (5) with primary and secondary chambers (11,12). A vent for liquid in the master cylinder in the event of an accident has connection between the chambers and an un-pressurized reservoir (13). The connection has a control (C) which operates at a set deceleration force to open the connection.

Description

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HYDRAULIC BRAKING SYSTEM FOR A MOTOR VEHICLE.

 The invention relates to a hydraulic braking installation for a motor vehicle, of the type which includes: - two braking circuits supplied separately by a master cylinder comprising a primary chamber and a secondary chamber respectively associated with a braking circuit and, in the primary chamber, a piston controlled by a rod actuated from a brake pedal, the master cylinder being supported by a wall located in front of the driver's legs, - and means for removing brake fluid from at least one chamber of the master cylinder to empty it, at least in part, during a collision in order to avoid a rise in the brake pedal.

 A braking installation of this type is known, for example from EP-BO 750 555. According to this document, the means for removing the brake fluid include chambers, or low pressure accumulators, into which the liquid pumped out of the cylinder master. This solution certainly makes it possible to avoid or limit a rise in the brake pedal in the event of a collision, but has the disadvantage of causing the pressure in the braking circuit to drop. To alleviate this drawback and maintain a residual braking action, it is indicated at the end of the document that the low-pressure accumulators are provided smaller than the pressure chambers of the master cylinder. However, even with such a measure, the level of braking remains lower than that of conventional braking. In addition, the limitation thus imposed on the volume of low pressure accumulators reduces their efficiency.

 The object of the invention is, above all, to provide a hydraulic braking installation for a motor vehicle, of the type defined above, in which the drawbacks mentioned above no longer occur or to a lesser degree.

 It is desirable, in particular, that the braking circuit concerned by the means for removing the brake fluid retains its braking capacity, without however obstructing the erasure of the brake pedal in the event of a frontal crushing.

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 It is also desirable that the solution proposed be simple, economical and reliable.

 According to the invention, a hydraulic braking installation of the type defined above is characterized in that the means for discharging the liquid comprise, for the chamber concerned of the master cylinder, on the one hand, a connection between this chamber and a pressurized brake fluid reservoir and, on the other hand, a means of controlling this connection, sensitive to a deceleration of determined value, this control means being able to take two positions, namely a first position, in normal vehicle operation, for which the connection between the chamber and the reservoir is cut, the braking circuit being supplied, and a second position, in the event of a collision causing a deceleration greater than the determined value, for which the connection between the chamber and the reservoir is established , while the braking circuit located downstream is isolated.

 The isolation of the braking circuit, relative to the reservoir and to the master cylinder, makes it possible to maintain or establish a pressure of the brake fluid in this circuit, without disadvantage in terms of the erasure of the brake pedal.

 The control means can consist of a two-position solenoid valve controlled by a deceleration sensor, for example the sensor installed on an airbag.

 Advantageously, the installation includes means for reinforcing the braking in the isolated circuit in the event of a collision. An over-assistance is then obtained which is particularly advantageous in the case where a vehicle continues on its trajectory after having suffered an impact which has triggered means for discharging the liquid.

 The means for reinforcing the braking can comprise a high pressure hydropneumatic accumulator (in particular pressure greater than 20 bars) connected to the line for supplying pressurized liquid to the brakes of the circuit concerned, downstream of the control means and a means of setting accumulator service, sensitive to deceleration.

 The means for commissioning the accumulator may comprise an electrovalve provided between the accumulator and the line supplying the brakes with pressurized liquid, this electrovalve being

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 controlled as a function of the deceleration undergone by the vehicle and being able to occupy two positions, namely a first position, in normal operation, in which the solenoid valve is closed and prevents any communication between the accumulator and the driving of the circuit brakes, and a second position, in the event of a collision, allowing the circuit brakes to be supplied under pressure from the accumulator.

 Means for inflating the accumulator under pressure are provided. These inflation means may include a line connecting the inlet of the high pressure accumulator to a part of the braking circuit which is put under high pressure, with a non-return valve preventing any flow from the accumulator to said part.

 Advantageously, the braking installation comprises an ABS system (anti-lock braking system) which comprises, for each braking circuit, a hydraulic pump suitable for being driven by a motor when conditions requiring the intervention of the ABS system are detected, and a group of valves controlled by a computer according to indications provided by sensors to modulate the fluid pressure in the wheel brakes and ensure optimal braking avoiding blockage, the discharge of each pump of the ABS system being done downstream of the aforesaid means of control, on a line going to the brake cylinders of the circuit.

 In the event of a collision triggering the control means, the ABS system is isolated from the master cylinder. Advantageously, the hydropneumatic accumulator under pressure is connected to the discharge of the pump of the ABS system for the circuit considered, which pump constitutes the means of inflating the accumulator with interposition of the non-return valve.

 It is possible to provide, during each starting of the vehicle, a sequence of operation of the pump for inflation of the accumulator to a sufficient pressure. If necessary, provision may be made at regular intervals for the pump to operate in order to re-inflate the accumulator and maintain sufficient pressure in the latter.

 The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below in connection with an exemplary embodiment described with reference to the attached drawings, but which n is by no means

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limiting. In these drawings:
Fig. 1 is a diagram of a hydraulic braking installation according to the invention, in normal operation.

Fig. 2 is a diagram of the installation in the event of a frontal collision.
Fig. 3, finally, is a diagram of a possible transient phase in the event of a frontal collision.

 Referring to Fig. 1, a hydraulic braking installation 1 for a motor vehicle can be seen to actuate wheel brakes 2a, 2b for the front wheels, and 2c, 2d for the rear wheels.

Each wheel brake conventionally comprises a cylinder in which a piston can be moved by a pressurized liquid in order to apply a brake shoe against an element, disc or drum, linked in rotation to the wheel to be braked.

 The installation 1 comprises two braking circuits respectively 3,4 supplied separately by a tandem master cylinder 5. The circuit 3 comprises the brake 2b of the left front wheel and the brake 2d of the right rear wheel. The other circuit 4 comprises the brake 2a of the right front wheel and the brake 2c of the left rear wheel. In the example considered, the two circuits therefore have a cross configuration in X. Of course, another configuration is possible, for example that in which the circuit 3 corresponds to the two rear brakes and the circuit 4 to the two front brakes.

 The master cylinder 5 comprises a primary piston 6 controlled by a rod 7 actuated by a brake pedal 8. One end of the rod 7 is articulated on the pedal 8. A servomotor 9, in particular formed by a pneumatic vacuum capsule, is designed to amplify the force exerted on the pedal 8. The primary piston 6 is linked to the output of the booster 9 and, in this way, to the rod 7. The primary piston 6 can slide in the master cylinder 5. A piston secondary 10 is disposed in the master cylinder in front of the piston 6 and can also slide in the master cylinder. Considering the normal direction of progression of the vehicle, the master cylinder 5 is disposed in front of the pedal 8 and the assembly is oriented in the longitudinal direction of the vehicle.

 A primary chamber 11 filled with liquid is formed between the piston 6 and the piston 10; a spring 11a is disposed in this chamber between the two pistons. A secondary chamber 12, also filled with liquid, is formed between the piston 10 and the bottom of the remote master cylinder

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 of the piston 6. A spring 12a is disposed in the chamber 12. The two chambers 11, 12 of the master cylinder are connected to a reservoir of pressureless liquid 13, also called a cover, for supplying the chambers 11, 12 with liquid of brake.

 The master cylinder 5 with the booster 9 is supported by a wall 14 located in front of the legs J of the driver. The upper end of the pedal 8 is articulated on a bearing supported by the wall 14.

 The primary chamber 11 is connected by a pipe 15 to the primary braking circuit 3. The secondary chamber 12 is connected, on its output 12b, by a pipe 16 to the secondary braking circuit 4. A pressure sensor 17 is mounted on the pipe 15 and converts the pressure into an electrical voltage. The circuit 3 comprises a pipe 18 extending downstream the pipe 15, and dividing into two branches 18b, 18d connected respectively to the brakes 2b, 2d.

 The braking installation comprises an ABS (anti-lock braking) system which comprises a group 19 of valves (not shown) controlled by a computer 20 according to indications provided by sensors, in particular sensors 21a, 21b, 21c, 21d, of the speed of rotation of each wheel of the vehicle.

 The secondary circuit 4 comprises a pipe 22 which extends downstream the pipe 16 and which is divided into two branches 22a, 22c to supply the brakes 2a, 2c respectively.

 The pipes 18b, 18d, 22a, 22c pass through respective valves provided in group 19.

 The ABS system further comprises an electric motor 23 and, for each circuit 3,4 a corresponding pump P3, P4 suitable for being driven by the motor 23. This motor 23 is started when conditions require the intervention of the ABS system , for example when a wheel lock is detected by a sensor.

 The suction of the pump P3 is connected to the brakes 2b, 2d by a line 24 which is divided into two branches 24b, 24d. The branches 24b, 24d pass through a respective valve provided in group 19 and controlled by the computer 20. A non-return valve (not shown) is provided on the pipe 24 to allow flow from the brake cylinders towards the suction from pump P3 but to prevent reverse flow. The suction of the P3 pump is also

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 connected by a pipe 25 to the pipe 15, by means of a valve 26 with two positions and a channel, which is normally closed.

 The discharge of the pump P3 is connected by a pipe 27 to the pipe 18. A two-position solenoid valve 28, controlled by the computer 20 and normally open, is disposed on the pipe 18 upstream of the junction of the pipe 27 with the pipe 18. A non-return valve 29 is connected between the inlet and the outlet of the valve 28; the valve 29 allows the flow of the pipe 15 to the brakes 2b, 2d, and prevents flow in the opposite direction.

 In a similar manner to that described in connection with the pump P3, the pump P4 has its suction connected to the brake cylinders 2a, 2c by a pipe 30 which passes through the block 19 and which is divided into two branches 30a, 30c. In group 19, the branches 30a, 30c are provided with electrovalves, normally closed, controlled by the computer 20, while a non-return valve is mounted on the part of the pipe 30 located in group 19 to allow the suction by pump P4 but prevent back flow.

 A bypass pipe 31 is connected on one side to the pipe 30 and, on the other side, to the pipe 16. A solenoid valve 32, normally closed, is mounted on the pipe 31. The solenoid valve 32 is controlled by the computer. 20 the electrical connection being simply initiated in FIG. 1.

 A discharge orifice of the pump P4 is connected by a line 33 to the pipe 22 which supplies pressurized liquid to the brakes 2a, 2c. A two-position solenoid valve 34, controlled by 20 and normally open, is disposed on the pipe 22 upstream of the connection with the pipe 33 and downstream of the connection with the pipes 16 and 31. A non-return valve 35 is connected in bypass between the inlet and the outlet of the valve 34, this valve 35 authorizing the passage of liquid coming from the master cylinder towards the brakes 2a, 2c, and preventing flow in the opposite direction.

 A means E for evacuating the brake fluid from at least one chamber, namely the secondary chamber 12 in the example considered, is provided for emptying, at least in part, this chamber 12 during a collision. This makes it possible to avoid a rise in the brake pedal 8, in the event of a frontal crushing of the vehicle causing a retraction of the master cylinder 5, liable to injure the driver's legs.

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 According to the invention, the evacuation means E comprises, on the outlet pipe 16 from the secondary chamber 12 of the master cylinder, upstream of the connection of the pipes 22 and 31 with this pipe 16, a connecting pipe L between the chamber 12 and the reservoir 13 of pressureless liquid.

 A control means C of the link L sensitive to a deceleration of the vehicle is provided. The means C is suitable for closing the link L between the outlet 12b from the chamber 12 and the reservoir 13 in normal vehicle operation, for decelerations below a determined limit, while ensuring communication between the chamber 12 and the brakes 2a , 2c. On the other hand, if the deceleration exceeds the predetermined limit, in particular in the event of a frontal collision, the control means C opens the link L between the outlet 12b and the reservoir 13 and keeps the braking circuit 4 located downstream isolated; all communication is cut off between circuit 4 on the one hand, and chamber 12 and tank 13 on the other.

 The control means C is advantageously constituted by an electrovalve EV1 with two positions, and two channels. This EV1 solenoid valve is controlled by the computer 20 according to the deceleration sensed by a decelerometer 36 which sends its information to the computer 20. The decelerometer 36 can be the one which equips an airbag provided in the vehicle.

 In the normal position shown in Fig. l, the EVI solenoid valve establishes communication between the downstream part and the upstream part of the pipe 16 so that the chamber 12 of the master cylinder makes it possible to supply the brakes 2a, 2c. This configuration corresponds to normal vehicle operation.

 In the event of a collision causing a deceleration greater than the predetermined limit, the computer 20 controls the change of position of the solenoid valve EV1 which passes into the position illustrated in FIG. 2. The outlet 12b from the chamber 12 is then connected to the cover 13, while the downstream part of the pipe 16 and the braking circuit 4 are isolated from the outlet 12b. The cut-off or closure established in line 16, to isolate the circuit 4, makes it possible to maintain or increase the braking pressure in the circuit 4, without interference with the volume of liquid in the chamber 12.

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 Advantageously, means R are provided to reinforce the braking in the circuit 4 when the electrovalve EV1 has been actuated and that the circuit 4 is isolated from the output 12b.

 The means R comprise a high pressure hydropneumatic accumulator 37 (in particular pressure greater than 20 bars) connected by a pipe 38, provided with a non-return valve 39, to a hydraulic inflation means G. The valve 39 is arranged so as to allow the passage of liquid from the inflation means G to the accumulator 37 for an increase in pressure, but prohibits flow in the opposite direction. Advantageously, when the braking installation is equipped with an ABS system, the inflation means G is constituted by the pump P4 associated with the braking circuit 4. The pipe 38 is connected to another discharge orifice of the pump P4. If this pump has only one outlet, the pipe 38 is connected to the pipe 33.

 The means R further comprises an electrovalve EV2, controlled by the computer 20, installed on a pipe 40 which connects the accumulator 37 to the branches 22a, 22c supplying the brakes 2a, 2c. This pipe 40 is itself connected to the pipe 38 upstream of the valve 39. The electrovalve EV2 is of the two-position and one-way type.

In normal operation the EV2 solenoid valve is in the closed position as illustrated in Fig. 1; when it is actuated it passes into the position which makes the accumulator 37 communicate with the pipes 22a, 22c.

 The electrovalve EV2 is controlled by the computer 20 under the same conditions as EV1, that is to say that it is actuated when the deceleration of the vehicle exceeds a limit detected by the decelerometer 36.

 The computer 20 is advantageously programmed to control, each time the vehicle is started, an operating sequence of the electric motor 23 of sufficient duration to ensure the inflation of the accumulator 37 by the pump P4. If necessary, provision may be made to repeat such a sequence at determined time intervals. A more expensive solution would consist in providing a pressure sensor on the accumulator 37 to control the starting of the motor 23 and of the pump P4 when the pressure of the accumulator 37 becomes lower than a determined limit.

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 When a collision caused the actuation of the solenoid valves EV1 and EV2 as illustrated in Fig. 2, and when the ABS system is put into service, a cavitation phenomenon may occur when the pump P4 is aspirated. To ensure a supply of liquid to the pump P4, it is possible to provide in the program of the computer 20 for very short sequences, for example of the order of a few milliseconds, during which the solenoid valve EV1 returns to the position which establishes the connection with the downstream while the solenoid valve 32 passes into the open position, as illustrated in FIG. 3. After this brief sequence, the installation returns to the configuration in Fig. 2.

 In the embodiment described, only the circuit 4 is equipped with the valves EV1, EV2 and the accumulator 37. It is possible to provide similar means on the other circuit 3 so as to also empty the primary chamber 11 of the master cylinder in the event of a collision.

 However, the operation of the braking installation according to the invention is as follows.

 In normal use of the vehicle, at each start, the accumulator 37 is inflated by the initial sequence of operation of the engine 23 and of the pump P4. When the vehicle is moving normally, the engine 23 is stopped. The EV1 valve is in the position of FIG. 1, that is to say that it communicates upstream and downstream, while the valve EV2 is in the closed position.

 When the driver brakes by pressing the pedal 8, the force amplified by the pneumatic servomotor 9 is applied to the piston 6. The liquid under pressure from the chambers 11 and 12 actuates the brakes 2b, 2d, and 2a, 2c of the two circuits 3 and 4.

 When conditions for putting the ABS system into service are detected during braking, for example blocking of one of the wheels, the motor 23 is started and the valves 28 and 34 change position.

Braking is then taken over by the ABS system.

 If the vehicle collides and if a deceleration greater than the predetermined limit occurs, the sensor 36 sends information to the computer 20 which causes the valves EV1 and EV2 to be actuated.

These valves pass from the position of FIG. l to that shown in FIG. 2.

 The EVI valve connects the chamber 12 with the reservoir 13 which allows the liquid from the chamber 12 to be evacuated.

This avoids or limits a retreat of the rod 7 and a rise of the pedal 8

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 during a frontal crushing and a retreat of the master cylinder 5.

The EV1 solenoid valve also isolates the downstream part of the circuit 4 from the outlet 12b and from the reservoir 13, and prevents a pressure drop in the braking circuit 4.

 The valve EV2 is passed into the open position so that the pressurized liquid from the accumulator 37 can supply the branches 22a, 22c and the brakes 2a, 2c. This results in over-braking assistance insofar as the pressure of the accumulator 37 is greater than that prevailing in the branches 22a, 22c.

 Thus, the braking is maintained or even increased in the circuit 4, which improves the control of the vehicle without interfering with the liquid in the chamber 12, nor causing the rod 7 to recede. It is indeed possible that the vehicle, after a shock that triggered the EV1 and EV2 valves continues on its path.

 In addition, the ABS system remains operational after triggering of the EVI and EV2 solenoid valves to keep the vehicle in a straight line if it continues to run after an impact.

 The liquid replenishment sequence of the suction of pump P4, illustrated in Fig. 3, makes it possible to avoid any cavitation phenomenon.

 The solution of the invention is simple to implement, economical and effective.

 In the case of a vehicle fitted with an airbag, the triggering of such an airbag can prevent the driver from braking. The solution of the invention makes it possible to compensate for the absence of braking of the driver when the triggering of the electrovalves EVI and EV2 is ensured by the same decelerometer 36 as that of the air cushion.

Claims (12)

CLAIMS 1. Hydraulic braking installation for a motor vehicle, comprising: - two braking circuits (3,4) supplied separately by a master cylinder (5) comprising a primary chamber (11) and a secondary chamber (12) associated respectively with a circuit brake and, in the primary chamber, a piston (6) controlled by a rod (7) actuated from a brake pedal (8), the master cylinder being supported by a wall (14) located in front of the legs of the driver, - and means for removing (E) the brake fluid from at least one chamber (12) of the master cylinder to empty it, at least in part, during a collision in order to avoid a raising the brake pedal (8), characterized in that the liquid discharge means (E) comprise, for the chamber (12) concerned of the master cylinder, on the one hand, a connection (L) between this chamber (12) and a reservoir (13) of pressurized brake fluid and, on the other hand, a control means (C) of this link, sensitive to a deceleration of determined value, this control means (C) being able to take two positions, namely a first position, in normal operation of the vehicle, for which the link (L) enters the chamber (12) and the reservoir (13) is cut, the braking circuit (4) being supplied, and a second position, in the event of a collision causing a deceleration greater than the determined value, for which the connection (L) between the chamber (12) and the reservoir (13) is established, while the braking circuit (4) located downstream is isolated. 2. Braking installation according to claim 1, characterized in that the control means (C) consists of a solenoid valve (EV1) with two positions controlled by a deceleration sensor (36). 3. Braking installation according to claim 2, characterized in that the deceleration sensor (36) is that installed to control an airbag. 4. Braking installation according to one of claims 1 to 3, characterized in that it comprises means (R) for reinforcing the braking in the circuit (4) isolated in the event of a collision. <Desc / Clms Page number 12> 5. Braking installation according to claim 4, characterized in that the means (R) for strengthening the braking comprise a hydropneumatic accumulator (37) high pressure connected to the supply line (22,22a, 22c) in liquid under brake pressure (2a, 2c) of the circuit (4) concerned, downstream of the control means (C), and a means of commissioning (EV2) of the accumulator, sensitive to deceleration. 6. Braking installation according to claim 5, characterized in that the means for commissioning the accumulator (37) comprises an electrovalve (EV2) provided between the accumulator (37) and the pipe (22, 22a, 22c) supplying the brakes with pressurized liquid, this solenoid valve (EV2) being controlled as a function of the deceleration experienced by the vehicle and being able to occupy two positions, namely a first position, in normal operation, in which the solenoid valve (EV2) is closed and prevents any communication between the accumulator (37) and the line (22,22a, 22c) of the circuit brakes, and a second position, in the event of a collision, allowing the brakes (2a, 2c to be supplied under pressure) ) from the circuit from the accumulator (37). 7. Braking installation according to claim 5 or 6, characterized in that the pressure in the hydropneumatic accumulator (37) is greater than 20 bars. 8. Braking installation according to one of claims 5 to 7, characterized in that inflation means (G) of the accumulator (37) are provided. 9. Braking installation according to claim 8, characterized in that the inflation means (G) comprise a line (38) connecting the inlet of the high pressure accumulator (37) to a part of the braking circuit (4 ) which is put under high pressure, with a non-return valve (39) preventing any flow from the accumulator towards said part. 10. Braking installation according to one of the preceding claims, <Desc / Clms Page number 13>  comprising an ABS system which comprises, for each braking circuit, a hydraulic pump (P3, P4) suitable for being driven by a motor (23) when conditions requiring the intervention of the ABS system are detected, and a group (19) of valves controlled by a computer (20) according to indications provided by sensors for modulating the fluid pressure in the wheel brakes, characterized in that the discharge of each pump (P3, P4) of the ABS system is done downstream of the above-mentioned control means (C) on a line (18, 22) going to the cylinders of the circuit brakes. 11. Braking installation according to all of claims 9 and 10, characterized in that the hydropneumatic accumulator (37) is connected to the discharge of the pump (P4) of the ABS system for the circuit considered (4), which pump constitutes the inflation means (G) of the accumulator (37) with interposition of the non-return valve (39). 12. Braking installation according to claim 11, characterized in that a sequence of operation of the pump (P4) is provided at each start of the vehicle for inflation of the accumulator (37) to a sufficient pressure.